A couple months of sailing with Druuchi may already reveal enough horrors to match a full army tour. Even if we know the destination is somewhere we don't care about, joining up with the slavers, torturers and death cultists is not worth it.
To be fair...isn't Sigmars empire really only(barely) lacking the first on that list with witch hunters being more than willing to torture and Morrites following a god of death explicitly?
Not that that's great but this doesn't actually sound like all that alien territory for our protagonist. Our protagonist who is an assasin, thus a trained murderer and who has at least turned one elf over to what was likely to involve torture.
Slavery would be (somewhat)abhorrent to her but I'm kind of confused on the other points.
. The Druchi are objectively the worst people who are not Chaos marauders or unliving corpses who see people as cattle.
I personally think Malekith and Morathii's horrid social experiment is legitimately the worst. Not competing for it.
Why?
Well for starters as you said vampires tend to view other people as either Irrelevant, as cattle or at least as obligated to them as their betters, barring the nechrarch's in the former category this at least means they don't tend to work people to death for the sake of not lifting their fingers.
It's rare but they are at least capable of being either decent rulers or living independently. I've certainly never seen the former from D'elves.
Chaos forces very often don't seem to serve their gods willingly but because of A: ''Better my neighbors get sacrificed than me'' B: ''This god is the only thing keeping my people alive'' or C: ''If I don't comply I'll be smited, possibly eaten by my god''
Yes there are exceptions, but a lot of chaotic factions and forces seem to march at gunpoint so to speak.
You could argue that the big M&M's in druuchiland don't provide their Elves with a choice, but they are not gods, Dark Elves have in fact been known to say defect to the wood elves, or go off to live mostly independently in the wilderness or even run operations not on Naggoroth at all.
Most of them seem very willing to be accomplices in the said regime, a regime that they didn't take apart or flee en mass from even when Malekith vanished for centuries so one cannot say they did not have a good shot at trying to be out of his clutches.
Or at least it reads that way to me.